Mueller's attorney told People.com Wednesday she underwent an operation for the dental problem this week.
"Brooke is in the hospital ICU related to the surgery for her impacted wisdom tooth," lawyer Yale Galanter told the magazine's Web site. "They are trying to get the infection and fever under control. The infection has spread."
Mueller and Sheen were ordered by a Colorado judge to stay away from each other following Sheen's Dec. 25 arrest for allegedly threatening and assaulting her.
Both parties reportedly are eager to put the incident behind them, resume their marriage and continue raising their 10-month-old twin sons together.
People.com said a court hearing in the matter was canceled Wednesday due to Mueller's illness.